As far as adopting them across the border, I think your best bet would probably be to contact the BLM Wild Horse and Burro department.
I can help you as far as trainability and such though.
I currently have 2 mustangs that I bought from adopters because they were too "wild" and the people were scared of them. Dobe was a 3 year old stud when I brought him home and had never been touched except to be branded and given his first round of shots. I was riding him on the second day and on the 5th day, I was using him on cattle. He never offered to buck and has made one hell of a nice horse. I think he is absolutely gorgeous even though his confo is a little iffy. I have been using him to work cattle for about 4 years and have roped and drug calves for branding during the last 2 springs. He was really spooky when I first started riding him but now he is my 'ride in the dark bareback with a halter' horse.
Koda had been handled a bit as a yearling by his adopter so he was not scared of people the way that Dobe was but he had not been taught anything. He would not lead, tie, pick up his feet, or anything that a semi-trained horse should do. He was a 4 year old when I brought him home and I didn't have time to work with him so I turned him out until he was 5. Last fall, I decided that it was time to use him so I caught him up. Within about 2 hours, I was riding him and he never offered to buck or anything. On the 3rd ride, I was using him through cattle and have been riding him sporadically over the last year. He is a nice horse but I just don't feel a connection with him so I am probably going to take him to a sale next spring (guaranteed no kill buyers).
This was me warming him up in the roundpen before I took him to the cattle on his 3rd ride.
And crappy as it is, here is a current pic of him.
I absolutely adore mustangs and I am with Iride, I would love to hear what your future plans are with the number you are looking to bring across the border.